In recent years, in order to reduce a burden on a driver, devices for giving various driving supports to the driver have been developed. For example, there is a device which detects a pair of white lines from an imaged image obtained by imaging the front side of a vehicle and which gives steering assist torque to a steering mechanism so that the vehicle travels along the center (target locus) of the lane formed by the pair of white lines (refer to Patent Citation 1). In steering control of this device, feedback control is performed. In this case, it is detected to what extent the actual vehicle position deviates from the target locus (that is, an error is detected), steering assist torque is calculated so that the error is decreased, and the steering assist torque is generated.
Patent Citation 1: Japanese Unexamined Patent Application Publication No. 11-321690
Patent Citation 2: Japanese Unexamined Patent Application Publication No. 2000-272592
Patent Citation 3: Japanese Unexamined Patent Application Publication No. 2000-177428